This updates kgb to work with both Python 2.x and 3.x. There were a

handful of changes needed to support 3.x, but they mostly amounted to

changes in attributes for functions and classes, the addition of one

more parameter for the CodeType constructor, and a switch to Unicode

strings.
This change does not support keyword-only arguments, which will require

additional work.

Ran unit tests on Python 2.7 and 3.5.